Isometric Resistance Exercise on Accelerated Atherosclerosis in Hypertension

• Introduction

Hypertension (HT) is the most common condition worldwide predisposing to atherosclerotic diseases (stroke, heart attack and peripheral vascular disease), apart from other traditional risk factors [1-3]. However, most HT patients have suboptimal BP control despite anti-HT medications [4]. On this issue, aerobic and dynamic exercise are effective in BP-reduction, but HT-patients often have poor compliance with exercise, mainly because of requirement of additional time, skill training, venue and equipments [5-6]. Isometric resistance exercised (IRE) (e.g. wall squat) may improve BP control, characterized by sustained muscle contractions with minimal change in muscle length and joint angle. However, most randomized trials of IRE have short duration and their long-term effect on BP-reduction, mechanisms and atherosclerosis complications, particularly in the Chinese, remain unknown [7-11].

Much advance in noninvasive vessel-imaging has been witnessed in past few decades. Brachial flow-mediated dilation (FMD) and carotid intima-media thickness (IMT), have been advocated as surrogate markers for the documentation of early atherosclerosis and evaluation of preventive measures (12-20). Both brachial FMD and carotid IMT can now be measured accurately with high reproducibility, and have been related to cardiovascular outcomes. In clinical context, a 0.1mm increase in carotid IMT has been associated with 41% increase in stroke and 43% increase in acute myocardial infarction over a follow-up period of 2-7 years. [17] An 8% difference in carotid IMT was approximately similar to the kind of difference seen between diabetes and non-diabetes Chinese adults [21).

• Aims and Hypotheses to be Tested

Systemic hypertension has been proven accelerating atherosclerotic process. To further test this initial hypothesis, this interventional substudy aims:

(i) To evaluate the impact of IRE on Clinic and Ambulatory BP (AMBP) in Hong Kong.

(ii) To evaluate the impact of IRE on atherosclerotic surrogates (brachial FMD and carotid IMT).

(iii) To evaluate the impact of IRE on mechanisms of BP and atherogenesis reductions, including endothelial function FMD, carotid IMT and arterial wall stiffness (cfPWV), and inflammatory parameters.

• Plan of Investigation The brachial FMD and carotid IMT before and after IRE intervention will be compared between the wall-squat and control intervention groups.

3.1 The impact of Isometric resistance exercise (IRE) Intervention on brachial FMD and carotid IMT.

Subjects:

200 HT adults, aged 18-75yr with SBP 135-160mmHg on AMBP will be recruited. Those with incapacitating osteoarthritis of knee and secondary HT will be excluded.

3.2 Methods: These HT participants will be randomized to practise IRE (100 adults) 14 mins per session, (2 mins IRE x 4sets, 2 mins rest in between), 3 sessions per week, or usual standard care & stretching (yoga) exercise (100 adults).

Week-0 ~ Health Examination, Randomization (IRE vs Yoga), Vascular Study (FMD & IMT), Blood Test, and Arterial wall stiffness (cfPWV)

Week-13 ~ Compliance (adhenence) checking

Week-24 ~ Health Examination, vascular study (FMD & IMT), blood tests, and arterial wall stiffness (cfPWV)

One Year ~ Compliance (adherence) checking, vascular study (FMD & IMT), vessel wall stiffness, and blood Tests

• Collection of health data:

• Questionnaire - All adult subjects will be interviewed and required to complete a detailed questionnaire regarding their individual and family history of cardiovascular diseases, hypertension, diabetes and current use of medications. Information on socio-economic status, tobacco use and lifestyle will be collected.
• Health examination - Each participant will receive a health examination and their weight and height, blood pressures, body mass index (BMI) and wait-hip circumference ratio (WHR) will be measured (light clothing and no shoes).
• Blood tests: 10ml of fasting blood will be taken for WBC platelet, fasting glucose, HgbA1C, low density lipoprotein cholesterol, hsC-reactive protein, fibrinogen and IL-6.
• Vascular Studies:

Endothelial function, flow-mediated dilation (FMD) of the brachial artery and carotid IMT will be studied by using high resolution ultrasound.

(i) Endothelial function, (brachial flow-mediated dilation, FMD) will be studied by using high resolution ultrasound, as described previously. [12,22-24] In brief, the diameter of the brachial artery will be measured on B-mode ultrasound images, using a linear array transducer (HF L38) with a median frequency of 13-6MHz and a standard Sonosite (MicroMaxx) system. Forearm tourniquet cuff placement will be applied to induce reactive hyperemia on deflation. Scans of brachial artery 10cm proximal to elbow will be acquired at rest, during reactive hyperemia (to induce flow-mediated endothelium-dependent dilation, FMD). FMD will be expressed as % of dilation from baseline vessel diameter normalized with vessel strain. Hyperemia is calculated as the % increase in blood flow after cuff deflation compared with baseline.

(ii) Carotid intima-media thickness (CIMT) measurement - B-mode ultrasound examinations will be performed using a 10-5 probe, with a 7.5 MHz scanning frequency linear array transducer. All carotid scans will be performed by a single operator after a predetermined, standardized scanning protocol for the right and left carotid arteries as described by Salonen and Salonen [16] and Touboul et al [19], using images of the far wall of the distal 10 mm of the common carotid arteries. All scans will be recorded on super-VHS videotape for subsequent off-line analysis for intima-media thickness (IMT), using a verified automatic edge-detecting and measurement software package as described previously. [19-24] The intra-observer variability of mean IMT is 0.003 to 0.011mm (CV 0.998%).

3.3 Outcomes

3.3.1 Primary outcomes: (i) Daytime ambulatory SBP and DBP (mean and BP variability) (mmHg) at baseline, 24 weeks and 1 year (ii) Vascular Parameters: Brachial FMD (%) and Carotid IMT (mm) at baseline, 24 weeks and 1 year.

3.3.2 Secondary outcomes: (i) Clinic BP and Ambulatory BP parameters (mmHg) at baseline, 24 weeks and 1 year.

(ii) Carotid femoral pulse wave velocity, cfPWV (mm/sec) at baseline and 24 weeks.

(iii) Other important traditional atherosclerosis risk factors: BMI (weight kg/ height m^2), glucose (mmol/l), lipid profiles (mmol/l), HgbA1-C (%), creatinine (umol/L), haemoglobin (g/dl), hsCRP (mg/l), Fibrinogen (mg/dl) and IL-6 (pg/ml) at baseline, 24 weeks and 1 year.

3.3.3 Safety profiles (if any) including CVS event and hospitalization at 1 year,

• Compliance with Declaration of Helsinki. The design, methodology and conduction of project are in compliance with Declaration of Helsinki.

• Data processing and analysis:

(5.1) Power Calculation: The Proc Power in the STS 9.2 statistical packages (SAS Institute Inc. Cary. NC, US) was used to calculate the sample size for FMD and carotid IMT. Data from our previous studies on Chinese adults in Hong Kong reported FMD was in 6-8% +/- 1.3%, and carotid IMT was 0.55-0.68mm +/- 0.1mm. On the assumption of post IRE brachial FMD will improve to 6.7-8.7 +/- 1.4%, and carotid IMT will reduce to 0.51-0.61mm +/- 0.11mm, recruitment of 200 Chinese adults (100 in each group) will be adequately powered (85%) to detect a group difference in brachial FMD of 1.2% and in carotid IMT of 0.06mm (12%), at 1 year between the two treatment groups.

(5.2). Data Analysis: Statistical Analysis System SPSS version 28 (SAS Institute Inc., Cary, NC, US) will be used for all statistical analyses. Descriptive methods will be used to describe characteristics of cardiovascular risks. The primary endpoints are AMBP, brachial FMD and carotid IMT; serological inflammatory biomarkers (Neutrophil/ monocyte ratio and Platelet), hsCRP, fibrinogen and IL-6 are secondary endpoints. Students' T-tests will be used to detect the group differences in brachial FMD and carotid IMT. Multivariable linear and logistic regressions will be used to calculate the risk magnitude by IRE vs usual care and stretching exercise interventions, and to control potential confounders such as traditional cardiovascular risk factors.

Inclusion criteria

• asymptomatic clinically stable adults
• aged 18-75 years
• Both genders
• Suboptimal BP (on stable medication) with SBP 135-160mmHG on ambulatory BP monitoring (AMBP)
• Agreeable to no drug changes in coming 1 year 24 weeks
• Agreeable to provide informed written consent form
• Agreeable to have AMBP and ultrasonic (FMD & IMT) scan third (baseline, 24 weeks and preferably 1 year)

Exclusion criteria

• relative contraindications to AMBP (e.g. atrial fibrillation)
• severe osteoarthritis of knee
• known secondary HT
• pregnancy/breastfeeding
• active malignancy
• Serious coronary profiles, (unstable angina), renal or hepatic derangement
• Need to change medications for control BP at 24 weeks ( SBP>160 mmHg)